Electronic circuit for triggering stroboscopic devices



A. C. ALLEN Sept. 5, 1950 ELECTRONIC CIRCUIT FOR TRIGGERING STROBOSCOPIC DEVICES 2 Sheets-Sheet 1 Filed Sept. 14, 1946 S P 1950 A. c. ALLEN 2,521,141

ELECTRONIC CIRCUIT FOR TRIGGERING STROBOSCOPIC DEVICES Filed Sept. 14, 1946 2 Sheets-Sheet 2 a ,4 y j I Z WIW JLQyS.

Patented Sept. 5, 1950 ELEGTRONIC CIRCUIT FOR TRIGGERING STROBOSCOPIC DEVICES Arthur C. Allen, Chicago, 111., assignor to Stewart- Warner Gorporation, Chicago, IlL, a corporation of Virginia Application September 14, 1946, Serial No. 697,141

9 Claims. 1 The present invention relates to a new. and improved electronic circuit and more particularly to a circuit adapted to modify an alternating current wave form so as to provide a single sharp essentially, means for locating the unbalance weight and determining its amount. It involves also a check of the rotating body after the application of corrective measures, such as the addition of a localized weight, to determine whether or not balance has been achieved.

In known types of apparatus, means engaging a support for the rotating body are provided to generate an alternating current having a definite phase relationship with the vibration of the support due to the unbalance of the rotating body,

the amplitude of which is approximately proportional to the amount of the unbalance. The apparatus also includes an electronic circuit for modifying the alternating current wave form to produce a single sharp peak or impulse occurring once each cycle, which peak is utilized to trigger or fire a strobotron tube. Because of the known predetermined relationship of the time of firing of the tube relative to the direction of vibration of the unbalanced body at that time, the locus of the unbalance is determinable by visual observation. The approximate amount of unbalance is determined by the measurement of the amplitude of the current generated by the vibration.

The present invention has for its object the provision of a new and improved electronic circuit for producing a triggering or firing impulse in a definite and substantially unvarying phase relationship with respect to an alternating current wave form.

A further object of the invention is to provide a new and improved electronic circuit of the character aforesaid wherein the impulse is utilized to fire a strobotron tube.

A further object of the present invention is to provide a new and improved electronic circuit including means for obtaining a firing impulse substantially at the point of maximum amplitude of an alternating current wave irrespective of the actual amplitude of the wave.

- Another object of the present invention is to provide a new and improved electronic circuit of a triggering or firing impulse relative to an alternating current wave in order that the impulse will occur substantially at the point of the maximum amplitude irrespective of the actual amplitude of the alternating current wave.

A further object of the present invention is to provide a new and improved electron circuit which will operate satisfactorily without blocking for high amplitude alternating current waves.

A still further object of the present invention is to provide a new and improved electron circuit including means for producing steep front impulses comprising an electron tube acting as a limiter.

Other objects and advantages of the present invention will become apparent from the ensuing description of an embodiment thereof, in the course of which reference is had to the accompanying drawings, in which:

Fig. 1 is a diagrammatic representation of on embodiment of the circuit of the invention; and

Figs. 2 to 10, inclusive, are graphs of the wave forms appearing at various points in the circuit, as indicated in Fig. 1.

As shown in Fig. 1, the electron circuit In of the present invention includes a pick-up [2 for generating an alternating current in response to vibrations induced in a rotatig body by unbal-v ance in the body. The alternating current generated by the pick-up I2 is supplied to the triggering pulse forming circuit and to an amplitude indicating meter [4. The pulse forming circuit includes a number of electron tubes l6, I8, 20 and 22, the functions and connections of which will be described hereinafter in greater detail and which control the firing of a strobotron 24.

The pick-up [2 may be of any suitable construction and is preferably of a type generating a relatively high voltage with a small excursion. As shown, diagrammatically, it includes a magnetic core 30 about which are wound a pair of coils 32 and 34, the former of which is connected to the meter through a full wave rectifier 3t and the latter of which is connected to the tube It through an input conducor 38. The pickup 12 includes also a permanent magnet structure as movably mounted adjacent the core 30 and which is operatively connected to a member 22 maintained in contact with a vibrating member, which may be a wheel axle or brake back plate. The vibrations of the unbalanced rotating body thus move the magnet Ail from and toward the core 30, thereby to generate alternating currents in the two coils 32 and 34 having a frequency depending upon the periodicity of the vibrations and an amplitude proportional to the amplitude of the vibrations. More specifically, the amplitudes are proportional to the instantaneous velocity of the magnet 40. The details of the construction of the pick-up [2 form no part of the present invention and will not be further described herein; and, it may be constructed as disclosed in Patent No. 2,383,405.

The character of the voltage generated in the winding 34 of the pick-up I2 is depicted by the curve 44 of Fig. 2. When the apparatus is used in connection with the balance of a wheel; it is desired to fire the strobotron 24 and thereby furnish a flash of light at the instant when the voltage, and hence the velocity of, the movable member (magnet 40), has maximum negative value. These firing times are indicated by reference characters 46 in Fig. 2. The timing of the firing instant must be independent of the frequency and amplitude of the armature vibration within the practical limits of the operation of the device, and this is. accomplished by the circuit of the present invention.

The alternating current voltage from the pickup I2 is supplied to thetube I6, which is preferably a section of a 6H6 tube, the other section of which is the previously referred to tube 22. The tube 15 operates as a half wave rectifier and it is connected preferably to be conductive only during the negative half cycles. Accordingly, its. cathode 48 is connectedto the input conductor 38'. while its anode 50 isconnectedto an output conductor 52.

Theoretically, the output or anode voltage would have the form indicatedJby the curve 54 in Fig. 3, from Whichit may be noted that only the negative half cycles of the input voltage appear in the output circuit. It will be noted also that the output voltage lags the input voltage by a phase angle indicated by the reference character 5.6, also in Fig. 3. Thislag results from the combination of the inductance of the pickup l2: and the. resistance-capacitance network in.

the anode circuit of tube l6,..t0. which reference will be had shortly, and this lag, is made use of in obtaining the triggering impulses at the desired time. The components-of; this portion of the; circuit are so proportioned thatthe phase lag is very nearly independent of the vibration frequency over the operating range of the apparatus which may be, from about three to fifteen cycles per second.

The tube l6, in accordance with one of the important features of the present invention, is arranged so that only portions,- of the negative half cycles appear on the output or load resistor 58 which is connected by conductor 60 to the grid 62.- of the first section of tube [8, which may be of the 6SL7 type. As a result of this arrangement the grid-,62 is supplied with spaced apart voltage pulses 64 (see Fig. 4) which begin at substantially the firing instants 46.

The circuit for providing-the pulses at substantially the firing instant includes not only thepick up [2 and the load resistor 58: but also the capacitor lificonnected between resistor 58 andthe anode 500i tube 16 andresistor 68 connected in parallel with theresistor 58 andcapacitor 66, i. e., connected acrossthe output of the. rectifier. The circuit including the resistors 58 and 68 and capacitor 66,-= acts as a sort of automatic volume control sothatonly the tips orpplses in the regionof the maximum amplisistor 94.

tudes of the negative half cycles pass through to the tube [8, which is utilized primarily as a limiter or peaking tube.

The resistor 58 may have a value of about 150,000 ohms, the resistor 68 a value of about 3.3 megohms; the capacitor 60 may have a capacity of about .5 mfd. and the pick-up [2 may have an inductance of about 87 henries and a resistance of about 18 to 20 thousand ohms.

The circuit between the rectifier l6 and limiter tube l8 also serves, in accordance with another feature of this invention, the function of preventing the first section of the limiter tube I8 from becoming blocked by the building of a high negative potential upon its grid 62. 0f the circuit elements, the capacitor 65 serves as a blocking condenser and the resistor 58 serves as a grid leak resistor and their values are such that the limiter tube does not become blocked.

A further feature of the invention is the utilization of the limitertube l8 to produce sharp and limited voltage changes in the anode circuit of the first section ofthe tube, which section includes a cathode 'lflandan anode '12 in addition to, grid 62. The tube i normally. biased by cathode resistor 14 (of about 2100 ohms) almost to cut-off and preferably so. that it. is driven to cut-off when the input signal has a low va1uesi1ch as about volt so that the limiter will be effectiveover a desired or normal range of; generated voltage. As the grid 62 becomes more negative in response to..the application of the more negative signal, (as indicated by curve 64), less current flows through the tube. The voltage drop across the plate resistor 16 (connected to the plateby conductor ll and having a value of about 220,000. ohms) thus decreases and, the. plate'|2. becomes more positive, thereby toproduce the signal pulses shown by curve 18 in Fig. 5. The plate. voltage rises sharply as indicated by reference character 18A but is thereafter limited and decreases (as shown at portion 'IBB-of the curve)-because of the action of bias resistor 14; When the fiow of current through the tube, decreases as a-result of the gradually increasing negative signal, the voltage drop across cathode resistor "decreases, with the result that the grid 62 becomesmore positive relative to the cathode and returns to its initial potential. When the signal decreases the plate voltage also decreases, as shown by the portion 780 of. the curve.

The signal pulses 18 are amplified bythe second section oftube- I8.to produce the pulses shown in Fig. 6, which are quitelike. the pulses l8 but-.of greater magnitude and oppositephase. The second section of the tube I3 includes a cathode 82, an anode 84:and.a grid86 coupled to the plate E2 of the first section through a capacitor 88, (ofabout .5 mid.) and the conductor ll. The cathode 52 is grounded through a bias resistor (of about 6800 ohms) and the. anode 84 is connected to a suitable source of anode voltagethrouglriconductor. Bland the plate re- The twoancdes. "and 84 are connected by a, bypass capacitor 9E-.-(of about .001 mid). A grid leakresistor 88 (of about-150,000 ohms) connects the grid 86-to ground.

The amplified negative,-;pulses BBHare differentiated bya differentiating circuit including the series connected capacitor-J fill-(of about .04 mid.) and resistor. I02. (ofeabout -3300 ohms) which are connected acrossthecutppt circuit of the second section oftube |8.; Thecapacitor. I00 -is--connected to conductorjland-theresistoris grounded. The output of the differentiating circuit-is supplied by conductor I04, connected to the junction of the capacitor I00 and resistor I02, to the grid I06 of tube 20, which is utilized as an amplifier and may be of the 6SK7 type, The differentiated pulse is indicated by the reference character I08 in Fig. 7 and it may be seen to include the relatively sharp and large magnitude negative pulses I08A and the smaller positive pulses I083.

The relatively sharp pulses I08 are amplified and inverted by the amplifier tube 20 which includes the previously referred to grid I06, and a cathode IIO connected to ground through bias resistor II2 (of about 500 ohms). The screen grid H4 is connected to a suitable source of potential through resistor II6 (of about 150,000 ohms) bypassed by a capacitor II8 (of about 8 mfd. and preferably of the electrolytic type). The suppressor grid I20 is connected to ground by conductor I22 and the anode I24 is connected to a suitable source of anode potential by conductor I26 and the primary winding I28 of a coupling and differentiating transformer I30, which is thus connected to the output or plate circuit of the tube 20.

The amplified pulses appearing in the plate circuit of tube 20 are shown by reference character I32 in Fig. 8. From this figure, it may be noted that the pulses consist of relatively high and sharp positive pulses I32A, and smaller and negative pulses I32B.

The differentiating and coupling transformer I30 is of the step-up type and has a step-up ratio of about 12 to 1. It includes a secondary winding I34, one terminal of which is preferably grounded and the other terminal of which is connected through resistor I36 (of about 47,000 ohms) to the rectifier 22, which eliminates the unwanted negative peaks. As previously indicated, the rectifier 22 is actually in the same tube envelope as the rectifier I6. It includes a cathode I38 connected to resistor I36 and an anode I40 connected to ground.

The voltage pulses appearing at the rectifier 22, i. e., across the cathode-anode circuit thereof are indicated by the reference character I42 in Fig. 9. These pulses are supplied to the strobotron 24 to fire it through a coupling circuit includin a small capacitor I44 (of about 470 mmf.) and resistor I46 of about 1 megohm) connected in series with each other and parallel to the rectifier 22. The capacito I44, which is preferably as small as possible and yet of a size to pass a suificient impulse to the strobotron 24,

serves to isolate the latter from the secondary winding I34, which would otherwise be conductively connected across the input. The junction of the capacitor and resistor is connected by conductor I48 to the control grid I50 of the strobotron 24. The coupling circuit modifies the pulses I42 somewhat to produce the pulses indicated by reference character I52 in Fig. 10, which may be noted to consist of the relatively high positive pulses I54 and the small negative pulses I56. The strobotron 24 is fired by the larger positive pulses.

Each time the strobotron tube is fired or rendered conductive a capacitor I54 (of about 4 mfd.), which is normally charged through a resistor I56 (of about 10,000 ohms) connected to a suitable source of potential is discharged through the tube 24. The discharge occurs through a circuit including conductor I58, the anode I60 and the cathode I62 of the strobotron 24. The shield grid I64 of the strobotron 24 is supplied with suitable potential by a voltage divider including the resistors I66 (of about 56,000 ohms) and I68 (of about 22,000 ohms), to the junction of which the grid I64 is connected.

When it is desired to use the apparatus of the present invention in connection with balancing a rotating body the magnet holding membe 42 is placed into contact with a member vibrated in response to the unbalance of the rotating body. For example, the member 42 may be maintained in contact with awheel axle or the back plate of a brake so that the magnet 40 is moved in response to the vibrations to generate :an alternating current having a sinusoidal wave form, as illustrated by reference character 44 in Fig. 2. In the succeeding portion of the description of the operation it is assumed that the input voltage thus applied to the cathode 48 of the rectifier I6 has a value of about 5 volts. This magnitude is readable upon the meter I4 which thus gives an indication of the amount of the unbalance.

The rectifier I6 and the modifying circuit including the resistors 58 and 68 and the capacitor 66 produce modified impulses 64 beginning substantially at the time the amplitude is a maximum, i. e., at the instant 46 when it is desired to fire the strobotron 24. The amplitude of these pulses, with a 5 volt input signal, is about .95 volt and the impulse is negative.

The negative pulses are limited by the first section of tube I8 to produce the pulses I8 illustrated in Fig. 5, which have an amplitude of about 18 volts. These pulses are amplified by the second section of tube I8 to provide the pulses illustrated in Fig. 6 having an amplitude of about volts. The pulses 80 are diiferentiated by the circuit I00 and I02 to produce the pulses I08, of which the negative portions have values of about 4 Volts and the positive portions of which have a positive value of about 1.5 volts. The sharp pulses I 08 are amplified by the tube 20 to produce the pulses I32 of which the positive portions have amplitudes of about 45 volts and the negative portions of about 11 volts.

The pulses I32 are differentiated by the transformer I30 and the negative portions are removed by the rectifier 22. The resulting positive pulses I42 have amplitudes of about 105 volts.

The positive pulses are supplied to the control grid I50 of the strobotron 24 through the coupling circuit I44, I46, which modifies the pulses somewhat to produce the pulses I52 of Fig. 10, of which the positive portions I54 have values of about 32 volts and the negative portions I56 of about 16 volts for the assumed input voltage.

Each time the strobotron is supplied with one of the pulses I52, which occurs at substantially the point of maximum amplitude of the generated wave, it is fired, thereby to illuminate the rotating body. By observing the apparent position of the rotating body, it is possible to determine the locus of unbalance in known manner and to correct the unbalance by the addition of a suitably located weight.

It should be understood that while but a single embodiment of the invention has been disclosed and described in detail that the details thereof are not intended to be limitative of the invention, except in so far as set forth in the accompanying claims.

Having thus described my invention, what I claim as new and desire to obtain by Letters Patent is:

1. In an electronic circuit for triggering a stroboscopic device in definite phase relation with an alternating current, the combination including, means including rectifying means supplied with the alternating current and energy storagemeans coupled thereto for providing current pulses of one polarity and occurring atv the regions of maximum amplitude of said current, a

stroboscopic device, and means including a peaking tube and limiting circuit, a first amplification and differentiation stage coupled to said tube, a second amplification and differentiation .stage coupled to said first stage, said means cou-- pled to said rectifying means for supplying a triggering impulse to the stroboscopic device for each of said current pulses.

2. In an electronic circuit for triggering a stroboscopic device in definite phase relation with an alternating current, the combination including, means including a rectifier supplied with the alternating current and passing only maximum amplitude portions of one polarity for providing current pulses of one polarity occurring. at the regions of maximum amplitude of said current, a stroboscopic device, and means including a peaking tube and limiting circuit, a first amplification and differentiation stage coupled to'said tube, a second amplification and differentiation stage coupled to said first stage, said means coupled to said rectifying means for supplying a triggering impulse to the stroboscopic device for each of said current pulses.

3. In an electronic circuit for triggering, a stroboscopic device in definite phase relation withan alternating current, the combination including, rectifying means supplied with the alternating current, andphase shifting meansconnected to said rectifying means for supplying current pulses of the one polarity at the regions of the maximum amplitude thereof, a stroboscopic device, and means including a peaking tube and limiting circuit, a first amplification and differentiation stage coupled to'said tube, a second amplification and differentiation stage coupled to said first stage, said means coupled to said phase shifting means for supplying a: triggering impulse to the stroboscopic devicefor each of said current-pulses.

4. In an electronic circuit for triggering; a stroboscopic device in definite phase relation with an lternating current, the combination including, rectifying means including a rectifier tube supplied with the alternating current for providing current of one polarity, means coupled to said rectifying means for supplying current pulses of the said one polarity at the region of the maximumamplitudes thereof, said means .including a. series connected capacitor and, resistor connected across said rectifier tube and a second resistor also connected across-said tube, a stroboscopic device, and means-including apeaking tube and limiting circuit, a first amplifica tion and differentiation stage coupled to said tube, a second amplification and differentiation stage coupled to said first stage, said-means'coupled to the junction of said capacitor and-firstmentioned resistor for supplying a triggering impulse to the stroboscopic device for each: of said current pulses. I

, 5. In an electronic circuit for triggering a stroboscopic device in definite phase relationiwith an lternating current, the combination including, rectifying means supplied with the alternating current for providing current of: onepolarity, a stroboscopic device, and meansincluding a limiter, a peaking, tube, a' first amplification-and differentiation stage. coupled to said tube, a second amplification and differentiation stage coupled to said first stage, and a coupling means between said rectifying means and said limiter including a capacitor acting as a blocking condenser and a resistor acting as a grid leak resistor connected to said tube for supplying a triggering impulse to the stroboscopic device for each of said current pulses.

6. In an electronic circuit for triggering a stroboscopic device in definite phase relation with an alternating current, the combination including, means including rectifying means supplied With the alternating current for supplying nega-- tive current pulses at the regions of the maximum amplitude of said one polarity of said a1- ternating current thereof, a stroboscopic device, and means including a peaking tube and limiting circuit, a first amplification and differentiation stage coupled to said tube, a second amplification and differentiation stage coupled to said first stage, said means coupled to said rectifying means for supplying triggering impulses to the stroboscopic device for each cycle of the alternating current and in definite phase relation thereto, said last-mentioned means including an electron tube having a cathode, a control electrode and a cathode bias resistor normally biasing the tube almost to cut off for limiting the resulting voltage changes.

7. In an electronic circuit for triggering a stroboscopic device in definite phase relation with an alternating current, the combination including, rectifying means supplied with the alternating current for providing negative current pulses, means associated with said rectifying means for supplying negative current pulses at the negative maximum amplitude regions of the alternating current, means coupled to lastmentioned means including an electron tube having a cathode, a control electrode and a cathode bias resistor for limiting the resulting voltage changes, a stroboscopic device, and means including a first amplifying and differentiating stage coupled to said tube and a second amplifying and differentiating stage coupled to said first stage for supplying a triggering impulse to the stroboscopic device for each cycle of said alternating current.

8. In an electronic circuit for triggering a stroboscopic device in definite phase relation with an alternating current, the combination including, a rectifier tube supplied with the alternating current for providing negative current pulses, means associated with said rectifying means including resistance and capacitance means for supplying negative current pulses at the regions of the maximum amplitude of said pulses, means coupled to said last-mentioned means including an electron tube having a cathode, a control electrode and a cathode bias resistor for limiting the resulting voltage change a stroboscopic device, and means including a first amplifying and differentiating stage coupled to said tube and a second amplifying and differentiating stage coupled to said first stage for supplying a triggering. impulse to the stroboscopic device for each cycle of said alternating current.

9. In an electronic circuit for triggering a stroboscopic device in definite phase relation with an alternating current, the combination including, means including rectifying and phase shifting means supplied with the alternating current for providing current pulses of one polarity and occurring at the regions of maximum negative amplitude of the alternating current, a

stroboscopic device, and means including a peaking tube and limiting circuit, a first amplification and differentiation stage coupled to said tube, a, second amplification and differentiation stage coupled to said first stage, said means coupled to said rectifying means for supplying triggering impulses to the stroboscopic device for each of said current pulses.

ARTHUR C. ALLEN.

10 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,306,791 Moe Dec. 29, 1929 2,449,651 Hathaway Sept. 21, 1948 

